1. Field of the Invention
This invention is related to the field of integrated circuits and, more particularly, to receiver circuits in integrated circuits.
2. Description of the Related Art
Integrated circuits generally include core circuitry that implements the operation for which the integrated circuit is designed, driver circuitry to drive output signals from the integrated circuit to external circuitry, and receiver circuits to receive input signals from external circuitry. The driver/receiver circuitry buffers and isolates the core circuitry from the external circuitry, handling the larger loads, higher current flows, higher voltages, noise, etc. involved in external communication.
Originally, the core circuitry operated with the same power supply voltage as the driver/receiver circuitry. However, as semiconductor fabrication technology continued to evolve and transistor feature sizes continued to be reduced, the core circuitry eventually required power supply voltages lower than those that could be used for communicating with the external circuitry. In some cases, backward compatibility with legacy external circuitry that was not manufactured using the most advanced semiconductor fabrication technology was desired. In other cases, a higher communication voltage is required by the effects of noise and other factors that affect the reliability of external communications.
Additionally, to support high speed interfaces, improve power characteristics, and/or to improve noise handling, some integrated circuit interfaces include differential signaling. In some cases, an interface can permit both differential and non-differential (single-ended) signaling. For example, the mobile double data rate 2 (mDDR2) memory interface (sometimes referred to as the low power DDR2 (LPDDR2) interface) permits single ended data signaling with a differential clock, or vice versa. Configurations that use only differential or only single ended signaling are also supported. Since the data is referenced to the clock, the integrated circuit that receives the data must account for the difference in delay for receiving differential inputs and single-ended inputs. The margin needed for the difference in delays can pressure the timing margins in the integrated circuit.